Cryo treating my blade at a later date

jmforge

Well-Known Member
Right. Unlike heat, more cold isn’t going to hurt it, so it’s always better to go with more cold. Dry ice does help a lot, it’s got a far better conversion rate than just chucking it in your freezer, but the LN is the best you can do. A 10 liter Dewar is only about $400, the LN is actually cheaper than dry ice, and mine will hold liquid for about a month. To the OP, if you are doing stainless, you might want to look into getting a Dewar. Plus, it’s fun to freeze weird things in LN and smash them:))
My problem is that I would need a 25-30 liter dewar with the big mouth as most of the limited number of stainless knives that I have done have been rather large kitchen knives. I could have dont most of them with dry ice. because they were AEB-L, but I sent them to Peters in one giant batch a couple of years back along with another batch of 3V blades. I don't know if I have any plans to use anything more complex than AEB-L in the forseeable future. I may have to just knuckle down and do that stuff myself. $15 a blade is a bit pricey for heat treating a simple "commodity" steel. I have hesitated because I had never changed the coils on my oven until I had to replace the controller. last year. 14 years. Never had the oven much above 1600F.
 

CDHumiston

KNIFE MAKER
Ya, pretty much any stainless stuff. D2, and A2 should have it, although they CAN be heat treated without it. Dozier’s work is a good example. There is no real need to avoid them, you can have someone heat treat them for you, or you can get into cryo for probably less than a grand. Once you start working with high alloy steels though, a real heat treat furnace is a must. Don’t even waste your time trying to do it in a forge.

I have a brand-new Paragon oven. But I really don't want to get into the liquid nitrogen game.

I have done some AEB-L, D2 and 440C without cryo. The blades test very well hardness wise.

What am I loosing without the cryo?
 

tkroenlein

Well-Known Member
To offer an opinion on where you're at with picking steels and deciding processes.

I've read everything I can read and watched what I can watch and studied all the graphs I can stand because I want to add what appears to be on the simpler end of steels, AEB-L and A2. I've decided that I will do LN cryo. I have to rearrange how I build altogether, batching HT and getting many profiled blanks ready, getting the LN and then marathon HT until I have many hardened blanks done, just to mitigate the cost and hassle of the LN. If I HT like I do currently, I'd HT about 5 a month, and that'd probably work out to about $15 a blade. If I batch 25 that drops it to $3 blade. It's a significant but manageable cost up front, especially in either of those two steels.

The reason I've chosen to cryo is to get that last point and a half hardness or so. It is small but significant difference in fine edge stability everything I've worked with so far, so I'm banking that it ain't different with most anything else.
 

Smallshop

KNIFE MAKER
I love A-2. It's all I heat treat. I think the cryo makes it both harder and tougher (definitely harder as I pick up a point on average...sometimes almost 2...on the Rockwell test.)

Bear in mind if you pick up 3-5 points after cryo (as some guys on the interwebs have claimed) your HT recipe is missing something.

I have wasted so much LN it's criminal....and it's a 112 mile drive for me.(So great question OP) I have actually thought about running blades for a few months and then HT like Tkroelein was suggesting but so far have just managed to waste a bit less each time...lol.

Any place selling LN for bull semen storage will most likely sell to a knife maker. I didn't dance around when he asked what I do with it. I think he was looking to rent me some long term semen storage in the big tank. He did seem tickled that "another knife maker" was buying from him. He's in Great Falls Montana and there are some good makers there (Ed Caffrey prolly being top o' the heap) but I didn't ask 'cause he didn't offer...
 

CDHumiston

KNIFE MAKER
I heat treated 8 blades today.

1st 3 were D2. Preheat 1200° hold 15 minutes. Ramp to 1850° soak for 30 minutes. After one 2-hour temper at 350° blades are 61, 61 and 62.

2nd 3 were 440C. Preheat 1425° hold 15 minutes. Ramp to 1875° soak for 30 minutes. After one 2-hour temper at 300° blades are 61, 60 and 61.5.

3rd 2 were AEB-L. Preheat 1500° hold 15 minutes. Ramp to 1950° soak for 15 minutes. After one 2-hour temper at 350° blades are 60 and 62.

All blades were plate quenched in aluminum in their foil pouches then removed and put in the freezer for an hour. It's all I had.

I am now curious if I need the second 2-hour cycle in the temper oven.
 
Right. Unlike heat, more cold isn’t going to hurt it, so it’s always better to go with more cold. Dry ice does help a lot, it’s got a far better conversion rate than just chucking it in your freezer, but the LN is the best you can do. A 10 liter Dewar is only about $400, the LN is actually cheaper than dry ice, and mine will hold liquid for about a month. To the OP, if you are doing stainless, you might want to look into getting a Dewar. Plus, it’s fun to freeze weird things in LN and smash them:))
I’ve been using my heat treat oven for cpm154 and s35 @ 1950 for 30+ min. Dry ice and kerosene over night and temper twice @ 400 deg for 2 hours each. I don’t know for sure the RC outcome but I’m hoping the steel is approaching 58-59. What does any body think it might be? I’m going to start looking for a used dewar. As I said earlier I’m far enough away from this type of supplies it would be easier to use LN for 30 days at a time. My knife making is my winter work. Too busy ranching the rest of the year.
Well, it all boils down to how much retained austenite you have after heat treat. I use CPM154 for all my stainless stuff, so I’m pretty familiar with it. The problem you run into is, the martensite finish temperature (where the austenite has fully converted to martensite) is well below zero Fahrenheit. You “can” heat treat it without cryo and expect a decent hardness, but the retained austenite over time can convert to martensite which is then untempered. Also, the boundary between areas of austenite and martensite is highly unstable, and the combination of the two issues leads to a good chance that the blade can develop cracks down the road. If you want a good example of how much cryo can affect the steel, try heat treating two samples. After they are quenched, stick one in a vise and bend it. As quenched steel should shatter like glass, but I’ll bet you that your sample will bend like mild steel, even if a file still skates off it. Cryo the other, and try the same test. It should break just like you would expect hardened steel to. I know that many high alloy steels have two tempering options, a high temp option that doesn’t use cryo, and a low temp option that does. The high temperature option uses the higher temps to force conversion of austenite, the low temp option uses cryo to force conversion. Usually doing the high temp version is at a small sacrifice to toughness and corrosion resistance. I’ve not used S35V, so I don’t know if that is an option for you. I have not seen that option for CPM154, and have always stuck to the low temp tempers that Crucible recommended. It’s a really great steel, but unless you find a recommended high temp temper option, do not skip cryo, and do it immediately after quench.
I want to set myself up using LN. I only build 1-3 knives at a time. I don’t build Santoku knives too often. Would a 10L Dewar be a good size for that amount of cryo treatment work?
 

Edwardshandmadeknives

Well-Known Member
I’ve been using my heat treat oven for cpm154 and s35 @ 1950 for 30+ min. Dry ice and kerosene over night and temper twice @ 400 deg for 2 hours each. I don’t know for sure the RC outcome but I’m hoping the steel is approaching 58-59. What does any body think it might be? I’m going to start looking for a used dewar. As I said earlier I’m far enough away from this type of supplies it would be easier to use LN for 30 days at a time. My knife making is my winter work. Too busy ranching the rest of the year.

I want to set myself up using LN. I only build 1-3 knives at a time. I don’t build Santoku knives too often. Would a 10L Dewar be a good size for that amount of cryo treatment work?
Ya, 10 L should be plenty. Check that the mouth diameter is sufficient for your work before you buy one. Most are just a hair under 2 inches
 

fitzo

Gold Membership
Fritzo look for Semen services. I get liquid nitrogen at REI. Reproductive Enterprises International. it is always spooky to me to see the gals dipping a plastic pitcher intoa 500 gallon vat and filling my semen tank with it.

Thanks! Another keyword pair to search. Appreciate it.
 

fitzo

Gold Membership
Fitzo you might want to be careful searching that. Might end up seeing something weird :D

Yeah, really! Gotta say, I didn't find any breeder services for cattle, but there seems to be a fertilization clinic on every corner. Not to mention the offers for short term employment. "Inspirational literature provided!" :rolleyes:
 

jmforge

Well-Known Member
Yeah, really! Gotta say, I didn't find any breeder services for cattle, but there seems to be a fertilization clinic on every corner. Not to mention the offers for short term employment. "Inspirational literature provided!" :rolleyes:
I was wondering what a search for "semen services" might turn over in an urban area? LOL
 

jmforge

Well-Known Member
I’ve been using my heat treat oven for cpm154 and s35 @ 1950 for 30+ min. Dry ice and kerosene over night and temper twice @ 400 deg for 2 hours each. I don’t know for sure the RC outcome but I’m hoping the steel is approaching 58-59. What does any body think it might be? I’m going to start looking for a used dewar. As I said earlier I’m far enough away from this type of supplies it would be easier to use LN for 30 days at a time. My knife making is my winter work. Too busy ranching the rest of the year.

I want to set myself up using LN. I only build 1-3 knives at a time. I don’t build Santoku knives too often. Would a 10L Dewar be a good size for that amount of cryo treatment work?
By most accounts, you only need to leave the steel in the dry ice/kerosen long enough for the blade temp to stabilize.
 
Ya, 10 L should be plenty. Check that the mouth diameter is sufficient for your work before you buy one. Most are just a hair under 2 inches
Many thanks for all your help. I’ve got one coming
Ya, 10 L should be plenty. Check that the mouth diameter is sufficient for your work before you buy one. Most are just a hair under 2 inches
I’ve read somewhere that I don’t necessarily need to fill the 10L canister full. Does this mean the knife blade does’t need to be submerged completely and just suspended with the lid closed? How long should the knife be in the canister?
 

jmforge

Well-Known Member
Many thanks for all your help. I’ve got one coming

I’ve read somewhere that I don’t necessarily need to fill the 10L canister full. Does this mean the knife blade does’t need to be submerged completely and just suspended with the lid closed? How long should the knife be in the canister?
That is what I have read also. As far as how long it needs to be in there, until it gets cold enough. Leaving the blade in for a long time may lead to the formation of eta carbides, but there is some debate as to how those may impact toughness., perhaps negatively.
 

Edwardshandmadeknives

Well-Known Member
From what I have read, the conversion from austenite to martensite happens very quickly, as in just a few seconds. Personally, I usually heat treat towards the end of the day, and just leave them in till the next morning. Probably around ten hours, depending on how late I sleep
 

fitzo

Gold Membership
If you use headspace cooling suspended above the liquid, I'd give it hours (overnight) to equilibrate. Make sure the styrofoam plug is in the top.
 
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